Light shutter system utilizing an image intensifier tube



July 22, 1969 B. w. MANLEY 3 7, 5

LIGHT SHUTTER SYSTEM UTILIZING AN IMAGE INTENSIFIER TUBE Filed June 24,1968 IN VENTOR. BRIAN W. MANLEY #16. AG NT United States Patent3,457,451 LIGHT SHUTTER SYSTEM UTILIZING AN IMAGE INTENSIFIER TUBE BrianWilliam Manley, Burgess Hill, England, assignor, by mesne assignments,to US. Philips Corporation, New York, N.Y., a corporation of DelawareFiled June 24, 1968, Ser. No. 739,542 Claims priority, application GreatBritain, June 30, 1967, 30,220/ 67 Int. Cl. H01 29/46, 29/56 US. Cl.315-14 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates toelectronic image intensifier devices. More particularly the inventionrelates to channel intensifier devices and to electronic imaging tubesemploying such devices. Such devices are secondaryemissiveelectron-multiplier devices comprising a matrix in the form of a platehaving a large number of elongated channels passing through itsthickness, said plate having a first conductive layer on its input faceand a separate second conductive layer on its output face to actrespectively as input and output electrodes.

FIGURE 1 illustrates a proximity-type channel intensifie-r tube.

FIGURE 2 illustrates the switchable shutter control circuit used in theintensifier tube of FIGURE 1.

Secondary-emissive intensifier devices of this character are described,for example, in British patent specifications Nos. 1,064,073, 1,064,074,and 1,064,076.

In the operation of these intensifier devices (when incorporated inelectronic imaging tubes) a potential difference is applied between thetwo electrode layers of the matrix so as to set up an electric field toaccelerate the electrons, which field establishes a potential gradientcreated by current flowing through resistive surfaces formed inside thechannels or (if such channel surfaces are absent) through the bulkmaterial of the matrix. Secondary-emissive multiplication takes place inthe channels and the output electrons may be acted upon by a furtheraccelerating field which may be set up between the ouput electrode and asuitable target, for example, a luminescent display screen.

An imaging tube or system employing such a device will be referred tofor convenience as an image intensifier tube or system rather than as animage converter tube or system even in applications where the primarypurpose is a change in the wavelength of the radiation of the image.

The patent specifications refer-red to above described inter 'alia imageintensifier tubes of the proximity type employing a channel intensifierdevice (an imaging tube of the proximity type is one in which thephoto-cathode is placed very near to the channel intensifier devicewithout intermediate electron-optical focusing means).

Such a proximity tube is shown schematically in FIG- URE 1 of theaccompanying drawing. In FIGURE 1 an object O is focused by an opticalsystem on to a photocathode P. Photo-electrons are liberatedsimultaneously "ice from all parts of the photo-cathode with varyinglocal intensities dependent upon the image.

The matrix of the device is usually of glass or other vitreous materialand its input and output faces are covered by first and secondconductive electrode layers E1-E2 respectively.

In each of the channels C that receives primary electrons at any giveninstant, multiplication takes place as described in the aforesaid patentspecifications and the necessary electric accelerating field is set upby connecting the electrodes E1E2 to a source shown schematically at B1.A further accelerating field is provided by a source B2 between E2 and aconductive coating (e.g. aluminum) associated with a luminescent screenS.

An additional source is shown schematically at B0 for directing theprimary electrons from P to flow towards the electrode E1 and its valueis such as to ensure adequate definition for any given P-El spacing. Inthe case of this proximity type of arrangement the photo-cathode P maybe very close to electrode E1 (for example 1.) and the voltage requiredfrom B0 may (unlike the voltage of B1 and B2) be very low, usually lessthan 100 volts.

It is an object of the present invention to exploit this last propertyso as to provide an improved light shutter system.

The invention provides a light shutter system comprising an imageintensifier tube of the proximity type including a channel intensifierdevice as herein defined, a photo-cathode facing the input electrode ofsaid device and a luminescent screen facing the output elect-rode ofsaid device, the shutter system comprising means for applying anaccelerating potential difference between said input and outputelectrodes, means for applying a further accelerating potentialdifference between said output electrode and said screen and controlmeans for causing shutter action by applying between said photo-cathodeand input electrode a controlling potential difference which hasselectively one or the other of two values, one value being such as toturn the tube off by causing the input electrode to repelphoto-electrons back to the photo-cathode while the other value is suchas to cause the flow of photo-electrons from the photo-cathode to theinput electrode.

Such a system can operate efficiently with very small changes in thecontrolling potential difference (P.D.) In a typical case, in order thatphoto-electrons should enter the channel plate, become multiplied andexcite the phosphor (on condition), a small positive potential withrespect to the photocathode is applied to the input electrode of thechannel plate. This will be less than 100 volts and may even in somecases be reduced to zero (although zero is not a desirable value). Toswitch the tube to the off condition and prevent photoelectrons enteringthe channel plate, a small negative potential is applied to the inputelectrode of the plate. This potential will generally be less than 10volts. A specific embodiment of the invention will now be described byway of example with reference to FIGURE 2 of the accompanying drawings.

In FIGURE 2, the proximity-type channel intensifier tube is showncomprising (as in FIGURE 1) a channel plate I with electrodes El-EZ, aphoto-cathode P and a luminescent screen S. Accelerating potentialsources are indicated again at B1 and B2.

The initial source B0 of FIGURE 1 is replaced by a switchable shuttercontrol circuit shown schematically as comprising a switch SW andalternative control potential sources Bcl-BcZ. Bc1 corresponds to theforward source B0 of FIGURE 1 and provides for electrode E1 a positiveON voltage in the range +1 to +100 volts. Source B02 provides for E1 anegative OFF voltage in the range 1 to 100 volts.

Although the photo-cathode P is shown earthed, it is possible to earthE1 instead, but the arrangement shown is preferably in spite of thesmall changes in the levels of elements E1E2S which occur when theswitch SW is actuated.

One practical set of values is given below by way of illustration asapplied to an arrangement of the type shown in FIGURE 2.

TABLE Spacing P-Ell 100a Spacing E1E2 mm 1 Spacing E2S mm 1 Diameter ofplate I mm 25 Diameter of channel 15 Voltage of B1 v 1000 Voltage of B2v 5000 Voltage of B01 v +100 Voltage of B02 v +100 Although the overalldimension of the channel plate I is given in the table as a diameter itis, of course, not necessary for the plate to be circular.

The control voltages given in the table (+100 and +100) are verysuitable values but other convenient values can be found in the range+25 to +300 for Bcl and 10 to 200 for B02.

What is claimed is:

1. A light shutter system comprising an image intensifier tube of theproximity type including a channel intensifier device as herein defined,a photo-cathode facing the input electrode of said device and aluminescent screen facing the output electrode of said device, theshutter system also comprising means for applying an acceleratingpotential difference between said input and output electrodes, means forapplying a further accelerating potential difference between said outputelectrode and said screen and control means for causing shutter actionby applying between said photo-cathode and input electrode a controllingpotential difference which has selectively one or the other of twovalues, one value being such as to turn the tube off by causing theinput electrode to repel photo-electrons back to the photo-cathode whilethe other value is such as to cause the flow of photo-electrons from thephotocathode to the input electrode.

2. A system as claimed in claim 1 wherein the two values of thecontrolling potential difference are within the range +25 v. to +300 v.and the range -10 v. to +200 v. respectively.

3. A system as claimed in claim 2 wherein the said two values aresubstantially equal to volts and 100 volts respectively.

References Cited UNITED STATES PATENTS 3,243,642 3/1966 Gebel 315-11RODNEY D. BENNETT, JR., Primary Examiner MALCOLM F. HUBLER, AssistantExaminer US. Cl. X.R. 31510, 11

